This application is based on Application No. 2001-025747, filed in Japan on Feb. 1, 2001, the contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to the valve timing control apparatus for an internal combustion engine for controlling the opening and/or closing timing of intake valves and/or exhaust valves of the internal combustion engine.
2. Description of the Related Art
In a valve timing control apparatus in which cam angles representative of the rotational positions of cams mounted on camshafts, respectively, for operating intake valves and exhaust valves are controlled to retard or advance with respect to the crank angle of a crankshaft of an internal combustion engine, it has been known in the past that when the amount of actual advanced angle is moving toward the amount of target advanced angle by more than a prescribed value, the calculation of an integral value is controlled to stop.
First, such known valve timing control will be described below. FIG. 2 is an explanatory view illustrating the phase shift range of a known valve timing control apparatus for an internal combustion engine represented by the relation between the amount of valve lift and the crank angle position of the crankshaft. In addition, FIGS. 4 through 6 are perspective views illustrating the internal structure, at a maximum retarded angle position, a locked position and a maximum advanced angle position, respectively, of a valve actuator provided with a variable valve timing mechanism (hereinafter referred to as a VVT mechanism) for individually varying the valve timing (i.e., opening or closing timing) of each of the intake valves and exhaust valves.
The valve timing is variable between a curve indicated by an alternate long and short dash line and another curve indicated by a broken line, as illustrated in FIG. 2. Such a variable range of the valve timing is determined by an operable or movable range of vanes 152 of the valve actuator within a housing 151, as illustrated in FIG. 4 to FIG. 6. FIG. 4 is a maximum retarded angle position of the vanes 152 relative to the housing 151, and FIG. 6 is a maximum advanced angle position thereof. The actuator is mounted on the camshaft for making the cam angle (i.e., the rotational position of the camshaft) variable relative to the crank angle (i.e., the rotational position of the crankshaft).
Next, a basic operation of this known valve timing control apparatus will be described according to flow charts of FIGS. 17 and 18 and a timing chart of FIG. 19. FIG. 17 illustrates a flow chart relating to the operation of the prior art. In FIG. 17, first in step 1701, the amount of an actual advanced angle VTd is detected from outputs of a cam angle sensor, which detects the cam angle of the camshaft, and a crank angle sensor, which detects the crank angle of the crankshaft. Then in step 1702, a proper target valve timing, i.e., the amount of a target advanced angle VTt suitable for engine operating conditions, is calculated. In step 1703, the actual advanced angle amount VTd is subtracted from the target advanced angle amount VTt to provide a control deviation VTe.
Subsequently, in step 1704, the control deviation VTe is multiplied by a proportional gain Pgain to provide a proportional value Ip. In step 1705, a difference between the current control deviation VTe and the last control deviation VTe(ixe2x88x921) is multiplied by a derivative gain Dgain to provide a derivative value Id. In step 1706, an integral value Ii is calculated.
The calculation of the integral value Ii is performed according to the flow chart of FIG. 18. That is, first in step 1801, when an absolute value |VTe| of the control deviation VTe is greater than an absolute value |VTe(ixe2x88x921)| of the last control deviation VTe(ixe2x88x921), it is determined that the actual advanced angle amount VTd does not follow the target advanced angle amount VTt. Then, in step 1802, the integral value Ii is added by the result of multiplication of the control deviation VTe and the integral gain Igain to provide an updated integral value Ii . Otherwise, when the absolute value |VTe| of the control deviation is less than the absolute value of the last deviation |VTe(ixe2x88x921)| in step 1801, nothing is done so the integral value Ii is not updated and the last value is maintained as it is.
Returning to FIG. 17, in step 1707, it is determined whether the absolute value |VTe| of the control deviation is equal to or less than a reference value VTh for determination of whether the actual advanced angle amount is in a steady state. When it is determined that the absolute value |VTe| is greater than the reference value VTh, then in step 1708, an output current value Iout is calculated by adding a holding current learned value Ih, the proportional value Ip, the derivative value Id, and the integral value Ii together. When it is determined in step 1707 that the absolute value |VTe| is less than the reference value VTh, the holding current learned value Ih and the integral value Ii are added to each other to provide an output current value Iout.
Thereafter in step 1710, the output current value Iout is converted into a corresponding duty value, which are output to oil control valves (OCVs). The oil control valves (OCVs) cooperate with an oil pump to constitute a hydraulic pressure supply system for controlling the oil pressure of each valve actuator to adjust the phase or angle of each corresponding cam and hence camshaft. The OCVs are represented by reference numerals 19 and 20 in FIG. 1 which will be later used to explain the present invention in detail. The internal structure of one of the OCVs is illustrated in FIGS. 7 through 9 for controlling the current to be supplied to a coil 193 thereby to perform the switching of oil pressure by the OCV.
Next, an actual operation of the above-mentioned known valve timing control apparatus will be described according to the timing chart of FIG. 19. FIG. 19 illustrates changes in the actual advanced angle amount VTd, the target advanced angle amount VTt, the output current value Iout and the integral value Ii. The target advanced angle amount VTt changes to the maximum advanced angle position at a time point 1901. Since a deviation between the target advanced angle amount VTt and the actual advanced angle amount VTd continues to be large until at a time point 1902, the OCV is controlled by the output current value Iout calculated by the operational expression at the time point 1708 of FIG. 17. At the time point 1902, the actual advanced angle VTd cannot follow the target advanced angle amount VTt. However, the VVT actuator is in a state fixed to the most or maximum advanced angle side, and hence it cannot be moved toward the advanced angle side any further. As a result, there still remains the deviation between the actual advanced angle amount VTd and the target advanced angle amount VTt.
From the time point 1902 to a time point 1903, the actual advanced angle amount VTd does not follow the target advanced angle amount VTt, so the integral value Ii is updated in a direction to increase. From the time point 1903 to a time point 1904, the integral value Ii is fixed to a preset upper limit integral value and exists in a state unable to increase any more. When the target advanced angle amount VTt changes to the retarded angle side at the time point 1904, the VVT actuator is controlled by the output current value Iout calculated in step 1708 of FIG. 16. However, since the integral value Ii was updated by mistake to an increasing side with the target advanced angle amount VTt being at the maximum advanced angle position, the actual advanced angle amount VTd cannot follow the target advanced angle amount VTt from the time point 1904 to the time point 1905, thus reducing the response.
Moreover, for example, Japanese Patent Application Laid-Open No. 7-229409 discloses another conventional valve timing control apparatus in which valve timing control based on a difference in phase between the crank angle and the cam angle is stopped at a high speed rotation of the engine, and instead valve timing is controlled by the maximum retarded angle. According to this prior art, in the case where the intake valve closing timing of an intake valve is made to be at the maximum retarded angle to retard the intake valve closing timing for the purpose of achieving the effect of inertia supercharging at a high speed rotation of the engine, an error in the detected phase difference between the crank angle and the cam angle grows greater as the rotational speed of the engine increases, and to prevent this, the control value is fixed at the maximum retarded angle during the high speed rotation of the engine.
With the known valve timing control apparatuses as described above, the range in which the valve timing can be varied is from the maximum advanced angle position to the maximum retarded angle position. Thus, there arises the following problem; that is, in case where even with the target advanced angle amount becoming the maximum advanced angle position, there remains a deviation between the actual advanced angle and the target advanced angle amount due to the fact that the actual advanced angle can not actually follow the target advanced angle amount owing to detection errors on the part of the means for actually detecting the valve timing, the insufficient working accuracy of the variable valve timing mechanism, etc., the integral value is updated so that the response reduces when the target advanced angle amount exceeds the maximum advanced angle position.
In addition, in the case where control is performed with the actuator being at a mechanical stop position thereof, the control position of the actuator becomes more stable when the actuator is controlled to be pushed against the mechanical stop position rather than when controlled in a feedback manner. Thus, there also arise the following problems; the detection errors on the part of the means for actually detecting the valve timing occur even in rotational speed ranges other than the high speed rotation range, and the insufficient working accuracy of the variable valve timing mechanism is an error factor irrespective of the number of revolutions per unit time of the engine.
The present invention is intended to solve the various problems as described above, and has for its object to provide a valve timing control apparatus for an internal combustion engine which is capable of ensuring not only good response when a target advanced angle amount is within a control range but also stability when the target advanced angle amount is out of the control range, thus providing durability without increasing the power capacities of a driving circuit and an OCV coil.
Thus, the valve timing control apparatus according to the present invention stops feedback control based on a deviation between a target advanced angle amount and an actual advanced angle amount, but performs control based on a fixed control value when the target advanced angle amount is out of a preset control range. In addition, updating an integral value is stopped and the integral value is not reflected on control when the target advanced angle amount is out of the preset control range. Otherwise, when the target advanced angle amount shifts from the outside of the control range into the control range, the integral value is initialized.
According to the present invention, there is provided a valve timing control apparatus for an internal combustion engine including: an intake valve and an exhaust valve being driven to operate in synchronization with rotation of the engine; an engine operating condition detecting section for detecting the operating conditions of the engine; a valve timing calculating section for calculating a target valve timing for at least one of the intake valve and the exhaust valve in accordance with the engine operating conditions; a variable valve timing mechanism for varying an opening timing and a closing timing of at least one of the intake valve and the exhaust valve; a valve timing detecting section for detecting an actual valve timing of at least one of the intake valve and the exhaust valve; a control amount calculating section for calculating a control amount based on the target valve timing, the actual valve timing and the engine operating conditions; an actual valve timing control section for outputting the control amount as an output control amount to the variable valve timing mechanism. Only when the target valve timing is within a prescribed control range, a control amount, which corresponds to a deviation between the target valve timing and the actual valve timing calculated by the control amount calculating section, is output as the output control amount to the actual valve timing control section.
In a preferred form of the present invention, when the target valve timing is outside the control range on a side where the control amount is set to a large value, the output control amount is equal to the sum of a holding control amount and a prescribed amount.
In another preferred form of the present invention, the holding control amount is the output control amount in a state in which the actual valve timing substantially matches the target valve timing when the target valve timing is within the control range.
In a further preferred form of the present invention, the valve timing control apparatus further includes a holding control amount learning section for learning the output control amount in a state in which the actual valve timing substantially matches the target valve timing when the target valve timing is within the control range.
In a yet further preferred form of the present invention, the output control amount is a current value for controlling the actual valve timing control section.
In a still further preferred form of the present invention, the holding control amount is set as a maximum control amount when the holding control amount learning section does not perform a learning operation.
In a further preferred form of the present invention, the maximum control amount of the holding control amount is a maximum value of a variation tolerance caused by the actual valve timing control section.
In a further preferred form of the present invention, the prescribed amount is set to the output control amount with which at least the actual valve timing is stopped at a mechanical stop position.
In a further preferred form of the present invention, when the control amount calculated by the control amount calculating section is greater than the sum of the holding control amount and a prescribed amount, or when the actual valve timing is within the control range, even with the target valve timing being outside the control range, the control amount calculated by the control amount calculating section is made as the output control amount.
In a further preferred form of the present invention, the valve timing control apparatus further includes an integral control section for integrating a deviation between the target valve timing and the actual valve timing to provide an integral correction value for correcting the control amount calculated by the control amount calculating section. The integral correction value is corrected to the control amount calculated by the control amount calculating section, and when the target valve timing is outside the control range, the control amount is set in such a manner as to inhibit the integral correction value from being updated.
In a further preferred form of the present invention, the valve timing control apparatus further includes an integral control section for integrating a deviation between the target valve timing and the actual valve timing to provide an integral correction value for correcting the control amount calculated by the control amount calculating section. The integral correction value is corrected to the control amount calculated by the control amount calculating section, and when the target valve timing is outside the control range, the control amount is set in such a manner as to inhibit the integral correction value from being corrected to the control amount.
In a further preferred form of the present invention, the valve timing control apparatus further includes an integral control section for integrating a deviation between the target valve timing and the actual valve timing to provide an integral correction value for correcting the control amount calculated by the control amount calculating section. The integral correction value is corrected to the control amount calculated by the control amount calculating section, and when the target valve timing changes from the outside of the control range into the control range, the integral correction value is initialized.